Oil circuit interrupter



May 20, 1947. w. M. LEEDS I OIL CIRCUIT INTERRUPTER Filed April 2, 19432 Sheets-$heet l fig. 1.

WETNESSES: I

INVENTOR IA/Z'UZ/Zmp M [4660 5.

BY 9\/ o ATM y 0, 1947. w. M. LEEDS 2,420,888

OIL CIRCUIT INTERRUPTER Filed April 2, 1945 2 Sheets-$heet 2 IIIWITNESSES: 2 1 INVENTOR 18 f5 16' MHZ/7P0; M Leeds.

Patented May 20, 1947 OIL CIRCUIT INTERRUPTER Winthrop M. Leeds,Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Application April 2,1943, Serial No. 481,529

6 Claims.

This invention relates to circuit interrupters in general and, moreparticularly, to circuit interrupters of the type which effect areextinction by a flow of are extinguishing fluid.

More specifically, it is an object of my invention to provide animproved circuit interrupter in which a movable contact cooperates witha relatively stationary contact to establish an arc. I associate a fluidmoving means with the stationary contact to assist in low currentinterruption, and I charge the fluid moving means by movement of themovable contact.

Another object is to provide an annular piston movable relative to astationary contact in a circuit interrupter and to charge the pistonduring the closing operation by the closing movement of the movablecontact.

My invention is especially suitable for use in circuit breakers of thetype which draw both a pressure generating arc and an interrupting arc,and which direct fluid under pressure from the pressure generating arctoward the interrupting arc to effect the latters extinction. I havefound that high speed oil circuit interrupters using a series connectedpressure generating arc to provide the energy for driving oil into themain interrupting break need a mechanically driven piston to supply thenecessary oil fiow during the interruption of low currents when the selfgenerated pressure produced at the pressure generating arc is inadequatefor high speed interrupting action.

I have found it desirable to associate an auxiliary spring driven pistonwith the intermediate contact because this type of construction resultsin the most advantages from the point of view of compactness in designand close proximity of the oil driving piston to the are beinginterrupted.

' A distinct advantage of my invention is the fact that the intermediateor relatively stationary contact need not travel at least the distanceof the piston travel, and consequently, the arcing gap opened by themain moving contact is not shortened by motion of the intermediate orstationary contact moving with the piston. In my invention I permitmovement of the piston relative to the intermediate or stationarycontact. Consequently, the main interrupting gap is not shortened andhigh speed operation is facilitated.

My invention has peculiar advantages as applied to circuit interruptershaving an interrupting time from the tripping of the operating mechanismto the time of arc extinction of only three cycles. In such fast circuitinterrupters it is particularly desirable that the main contact gap isnot shortened because of movement of the intermediate or relativelystationary contact with the piston.

Another object of my invention is to provide a passage through theintermediate or stationary contact of an interrupter which cooperateswith an annular piston which I dispose in surrounding relation withrespect to the intermediate or stationary contact. Preferably the pistonitself has an orifice which cooperates with the passages through thestationary contact to facilitate are extinction.

Another object of my invention is to provide an improved circuitinterrupter of the type which draws at least two arcs in series, and toprovide an improved intermediate contact construction which facilitatesready removal and inspection of the intermediate contact.

Another object is to provide an improved circuit interrupter of the typedrawing both a pressure generating arc and an interrupting arc withimproved venting means for cooling the intermediate contact.

Another object is to provide an improved circuit interrupter of suchconstruction that operation of the breaker without load serves to flushout the arcing chamber.

Another object is to provide an improved circuit interrupter in which apair of contacts cooperate to establish an are. I dispose piston meansin surrounding relation with one of the contacts and movable relativethereto, and I charge the piston means by the closing movement of theother cooperable contact.

Further objects and advantages will readily become apparent upon areading of the following specification taken in conjunction with thedrawings, in which:

Figure 1 is an elevational view, partially in section, of a circuitinterrupter embodying my invention and shown in the closed circuitposition;

Fig. 2 is an enlarged vertical section of one of the arc extinguishingunits shown in Fig. l, the unit being shown in the closed circuitposition;

Fig. 3 is a View similar to Fig. 2 but showing the disposition of theseveral parts during a circuit opening operation;

Fig. 4 is a fragmentary enlarged vertical sectional view taken on theline IV-IV of Fig. 2;

Fig. 5 is an inverted plan view in section taken on the line VV of Fig.2; and

Fig. 6 is a plan view in cross-section taken on the line VI-VI of Fig.2.

Referring to the drawings, and more particu- 3 larly to Fig. 1, thereference numeral I designates a tank filled to the level 2 with asuitable arc extinguishing fluid 3, in this instance circuit breakeroil. Depending from the cover 4 of the tank l are insulating bushings 5which enclose terminal studs 5. Threadedly secured on the terminal studs6 and clamped thereto are contact feet 1, which support areextinguishing units generally designated by the reference numeral 8.

Referring more particularly to Fig. 2 it Will be observed that the arcextinguishing unit 8 comprises a top dome casting 9 which forms apressure generating chamber generally designated by the referencenumeral 10. Disposed within the pressure generating chamber I is apressure generating contact II pivotally mounted at I2 and cooperablewith a relatively stationary or intermediate contact I3 to draw apressure generating are designated by the reference numeral 14 in Fig.3.

Also cooperable with the intermediate or stationary contact I3 is amovable contact I constituting the opposed outer ends of a conductingcross-bar I5. Referring to Fig. 3 it will be noted that the movablecontact I5 cooperates with the relatively stationary contact I3 to drawan interrupting are designated by the reference numeral I? in Fig. 3.The are extinguishing unit 8 comprises a plurality of suitably shapedinsulating plates secured in position by insulating tie rods IS. Theupper insulating plate 45 has a cylindrical bore therein for slidablyreceiving the stationary contact it. Contact I3 is provided with aflanged upper portion which engages the plate 45 and thereby positionsthe contact with respect to the plate when the contact structure is inthe open circuit position. The insulating plates form two vertical flowpassages generally designated by the reference numeral I9, whichcommunicate at their upper end with the pressure generating chamber I8,and which communicate at their lower end with a plurality of inletpassages designated by the reference numeral 28 and shown more clearlyin Figs. 2 and 6. The arc extinguishing fluid, in this instance oil,which is forced downwardly from the pressure generating chamher Itthrough the vertical flow passages I9 and through the inlet passage 20strikes the interrupting are I; and passes through orifices 23 ininsulating orifice plates 23a to exhaust through exhaust passagesdesignated by the reference numeral 2! and shown more clearly in Figs. 4and 6.

The pressure generating contact II is actuated by an insulatingoperating rod 24 which is guided in an aperture 25 provided in thebottom metallic plate 26 of the arc extinguishing unit 8. A compressionspring 2'! is disposed between the bottom plate 28 and a head 28integrally formed with the operating rod 24. Consequently, thecompression spring 21 biases the operating rod 24 in a downwarddirection as viewed in Fig. 2. Integrally formed with the operating rod24 is a flange 29 which serves as a lower seat for a compression spring38. The upper end of the compression spring 38 abuts against a washer 3|which is slidable on the operating rod 24. The washer 31 engages inabutting relation two actuating arms 32, only one of which is shown. Theactuating arms 32 serve to externally actuate the pressure generatingcontact II about the pivot 2. The actuating arms 32 are formed withrelatively wide apertures 33, through which extends a pin 34 rigidlysecured to and movable with the operating rod 24.

A flexible conducting strap 36 is secured by a screw to one of theactuating arms 32 and at its other end to the top dome casting 9.Consequently, the pivot I2 does not need to carry the breaker current.The conducting cross-bar I5 is reciprocally actuated in a verticaldirection, as viewed in Fig. 1, by an insulating operating rod 22, Inthe closed circuit position of the interrupter as shown in Figs. 1, 2and 4 the electrical circuit therethrough comprises the lefthandterminal stud 6, left-hand contact foot T, top dome casting 9,conducting strap 36, actuating arm 32, pressure generating contact I I,relatively stationary or intermediate contact I3, lower movable contactI5, conducting cross-bar I6, through the right-hand arc extinguishingunit 8 in a simila-r manner to the right-hand terminal stud 5.

When it is desired to open the electrical circuit passing through theinterrupter, or in response to overload conditions existing in thecircuit con-- trolled by the interrupter, suitable mechanism, not shown,is actuated to cause downward movement of the insulating operating rod22. The downward movement of the insulating operating rod 22 causesdownward movement of the movable contact I5. Since the compressionspring 21 biases the operating rod 24 in a downward direction, theoperating rod 24 will follow the downward movement of the conductingcross-bar IE to cause a clockwise rotation of the pressure generatingCOYltfiCt II about the pivot I2. The movable contact I5 separates fromthe stationary contact I3 at substantially the same time that thepressure generating contact II separates from the stationary contact I3to result in a substantially simultaneous drawing of both a pressuregenerating arc I4 and an interrupting are I "I, as shown more clearly inFig. 3.

If the current through the interrupter is high, the pressure formed atthe pressure generating arc I4 will correspondingly be high. If,however, the current being interrupted is low the pressure formed at thepressure generating arc I4 will also be low, and it will, therefore, bedinicult to provide the requisite amount of fluid under the desiredpressure to flow through the vertical flow passages I9, through theinlet passages 28 and toward the interrupting are I! to effect thelatters extinction.

To assist in the interruption of low currents through the arcextinguishing unit 8, I provide an annular piston member 4Isubstantially surrounding the intermediate or stationary contact I3 andshown more clearly in Figs. 2, 4 and 5. The piston member 4! has anaperture 42 formed therein which accommodates movement of the piston 4Irelative to the stationary contact I3. The aperture 42 provided in thepiston 4| contains an annular recess 43, the purpose for which willappear more clearly hereinafter.

A compression spring 44 biases the piston II in a downward direction,having as its lower seat the piston 4| and havin as its upper seat thetop insulating plate 45 of the arc extinguishing unit 8. It will beobserved that a passage 41 is provided in the stationary contact I 3which communicates with a transversely extending passage 48 also formedin the intermediate contact I3. The region back of the piston 4|,generally designated by the reference numeral 49, communicates throughthe vents 50 (see Figs. 4 and 5) to the region exterior of the arcextinguishing unit 8.

During the interruption of low currents through the interrupter, whenthe pressure created at the pressure generating arc I4 is low, thecompression spring 44 will force the piston 4| downwardly to drive theoil in the region below the piston 4| downward and through the exhaustpassages 2|. Also some of the oil displaced in the region 5| by thedownward movement of the piston 4| will move upward through the aperture42 provided in the piston 4| and through the passage 41, passage 48 tothe vents 59 (see Fig. 4) Thus the passages 41 and 48 also serve as aby-pass around the piston 4| to provide greater freedom of action.

Consequently, the construction which I disclose is operable not only toforce oil downward through the exhaust passages 2|, but is also operableto drive oil upward through the aperture 42 and through the stationarycontact I3 itself. The annular recess 43 provided in the piston 4|serves to increase the turbulence during the downward movement of thepiston 4| thereby enhancing arc extinction, and also increases theinsulation surface of the aperture 42 to minimize the possibility ofinsulation breakdown through the aperture 42 due to carbonization of theinsulation surfaces.

It will be observed that during the closing operation that the movablecontact |5 charges or raises the piston 4| to substantially the fullycharged position before the movable contact l5 causes final closedcircuit contact engagement, thereby placing the piston in readiness toforce fiuid toward the interrupting arc during a, subsequent openingoperation even if such operation is required immediately upon closingthe interrupter on a fault or a heavy overload. Consequently, durin theopening operation the piston 4| can move downwardly independently of thestationary contact l3 at a speed solely dependent on its driving spring44 and the resistance to the fiow of the oil displaced from the region5|.

Strictly speaking, any downward movement of the intermediate contact [3would tend to shorten the main gap and hence defeat one of the purposesof the invention, that is, to rapidly form the pressure and interruptinggaps, this being a fast three-cycle breaker. However, it is necessary topermit a slight upward movement of the intermediate contact I3 to enablethe compression sprin 36 to furnish the contact pressure not onlybetween the intermediate contact [3 and the movable contact l5, but alsobetween the intermediate contact l3 and the pressure generating contactII.

t is apparent that, should the intermediate contact l3 be fixedly heldin a fixed position, with the construction shown, two compressionsprings would be required for furnishing the proper contact pressurebetween the contacts I5, and the intermediate contact |3. But with theconstruction utilized, by permitting the slight upward movement of theintermediate contact l3, a single compression spring 30 suifices toprovide contact pressure between the several contacts. It will beobserved that the travel of the intermediate contact is is so slight asto inappreciably shorten the main interrupting gap during the openingoperation. This construction, therefore, does not permit the maincontact gap to be shortened by movement of the stationary contact itwith the piston 4|. The result is a constantly rapidly increasingcontact gap separation not only for the pressure enerating are H, butalso for the main interrupting are H. Thus the use of this constructionis particularly desirable in fast three cycle breakers, where thecontact gap must be increased very rapidly to prevent reignition of theextinguished are after a current zero.

It will be noted that the passage 41 provided in the stationary contact|3 together with the transversely extending passage 48 permits aventilation of the intermediate or stationary contact l3 in the closedcircuit position of the interrupter. This is especially desirable whenthe interrupter is carrying heavy load currents continuously for at thistime the intermediate or stationary contact I3 is the hottest part ofthe interrupter. facilitate ventilation of the intermediate contact I3but relieve back-pressure on the piston 4| to allow free operation ofthe iston 4| both during opening and also during the closing operations.

I provide a removable inspection plate 39 covering an opening in the topdome casting 9 to permit an operator to view the interior of thepressure generating chamber l0 and inspect the contacts withoutdisassembling the arc extinguishing unit 8. This has an additionaladvantage because with the construction shown the intermediate orstationary contact i3 may be removed from the unit 8 through the openingcovered by the inspection plate 39 without disassembling any of theparts of the arc extinguishing unit 8.

I also provide a check valve 31 which closes apertures 38 formed in thetop dome casting 9 during conditions of high pressure within thepressure generating chamber l0. Consequently, after a circuit openingoperation accumulated gas within the pressure generating chamber l0 mayescape out through the apertures 38 upon a lowering of the check valve31. The check valve 3? also cooperates with the piston 4| to result in acomplete flushing of the unit 8 during an opera tion of the interrupterwhen the interrupter is not carrying current. This results since on theclosing stroke the moving contact l5 has only a slight clearance throughthe orifices 23 thus eliectively closing the vents 2|, and oil is drawnin only through the check valve 31 by the suction action caused by theupward movement of the piston 4!. It will be noted that as the movingcontact l5 raises the piston 4| the moving contact i5 also effectivelycloses the passage 41 in the intermediate contact |3. Thus with thepassage 41 and vents 2| effectively closed, the only entrance for theoil is through the apertures 33 associated with the check valve 31.-

During the opening operation, with no load current passing through theinterrupter, the piston 4| will move downward to result in a closing ofthe check valve 31 and a forcing of oil through the exhaust passages 2|and the vents 50 to result in a flushing of the arc extinguishing 'unit8.

In the particular embodiment of my invention shown in the drawings theintermediate or sta-- tionary contact I3 is moved slightly upward by themovable contact I5 in the closed circuit position of the interrupter asclearly shown in Fig. 2. Consequently, the compression spring 35provides the requisite contact pressure not only between the pressuregenerating contact l and the intermediate or stationary contact |3. butalso between the intermediate contact l3 and the lower movable contactl5. During the opening operation the movable contact |5 and the operating rod 24 initially move down together, thus resulting in theintermediate contact l3 follow-- ing .the initial downward movement ofthe movable contact l5. Meanwhile the compression spring 30 maintainsthe pressure generating con- Also the vents 50 not only serve to.

tact H in abutting engagement with the intermediate contact I 3 untilthe pin 34 strikes the bottom of the apertures 33. When this occurs, theactuating arms 32 are positively driven downward by the pin 34, andsubstantially at this same time the movable contact l5 separates fromthe intermediate contact l3. Consequently, the pressure generating arcl4 and the interrupting are H are both formed substantiallysimultaneously. This provides a very fast rate of contact separationwhich is necessary for three cycle breakers.

The following table indicates the marked improvement on arcing time as aresult of using a piston as compared with interrupting without use of apiston. All of the data was taken on a 33 kv. circuit with a normalfrequency of 60 cycles and using only one unit 8 electrically connectedin the circuit, the second unit 8 being shunted It will be apparent froman examination of the above table that the performance of theinterrupter was greatly improved by using a piston associated with thestationary or intermediate contact 13.

Certain features of the oil passages, inlet passages and exhaustpassages together with certain features of the contact pressuremechanism herein described is disclosed and broadly claimed in a patentapplication by Leon H. Ludwig, Benjamin P. Baker and Winthrop M. Leeds,Serial No. 465,244, filed November 11, 1942, entitled Circuitinterrupters and assigned to the assignee of the instant application.

It will be apparent from the above disclosure that I have provided anovel piston arrangement especially suitable for high speed breakerswhich require rapid contact separation. If the arcing current is high,the pressure created at the pressure generating are 14 willcorrespondingly be high and the piston 4i may be prevented by the highpressure from moving downward. In this event, however, a piston wouldnot be necessary to obtain rapid arc extinction because of the highpressure already provided at the pressure generating arc I4. If,however, the arcing current is low, the piston M will move downward tocooperate with the pressure generating arc 14 to effect rapid extinctionof the interrupting are 11. During low currents the flow from the pistonwill tend to predominate over the now created by the pressure generatingarc. It will be apparent that with the piston construction disclosed thelower part or" the piston 4| may be used as an orifice with a portion ofthe oil flowing through the orifice 42, through the intermediate contact[3 itself to exhaust through the vents 50.

Although I have shown and described a particular structure, it is to beclearly understood that the same was merely for the purpose ofillustration and that changes and modifications may readily be made bythose skilled in the art without departing from the spirit and scope ofthe appended claims.

I claim as my invention:

1. In a circuit interrupter, a pressure-generating contact cooperablewith a relatively stationary contact to establish a pressure-generatingare, a movable contact arranged to make abutting engagement with thestationary contact in the closed circuit position and separabletherefrom during circuit opening to establish an interrupting arc, apiston member substantially surrounding the relatively stationarycontact and movable relative to said stationary contact, spring meansbiasing the piston member in a direction to move fluid under pressuretoward said interrupting arc to facilitate arc extinction, said movablecontact having a shoulder portion which engages the piston member duringthe closing stroke to charge the same against the biasing action exertedby the spring means before the movable contact strikes the stationarycontact in abutting engagement, and passage means provided in therelatively stationary contact for causing a flow oi fluid from theforward to the back side of said piston to facilitate piston movementduring the opening operation and extinction of the interrupting arc,said passage means also providing a vent for the circulationtherethrough of fluid when said interrupter is in the closed positionfor cooling said stationary contact.

2. In a circuit interrupter of the fiuid immersed type, contact meansincluding a substantially stationary intermediate contact forestablishing a pressure generating arc and an interrupting arc, saidarcs each having a terminal on opposite ends of said intermediatecontact, said pressure generating are causing a how of fluid againstsaid interrupting arc to assist in extinguishing the latter, an annularpiston surrounding said intermediate contact and mounted for relativemovement with respect to said contact, resilient means for biasing saidpiston in a direction to cause an additional flow of fluid against saidinterrupting are, means permitting the movement 01": said annular pistonbeyond the interrupting arc terminal end of said intermediate contactduring an opening operation to cause said piston to envelope a portionof said interrupting arc and assist in extinguishing the same, and meansintercoimecting said contact means and said piston during a closingmovement of said contact means whereby said contact means moves saidpiston against the biasing action of said resilient means tosubstantially charge the latter prior to the final closing movement ofsaid contact means.

3. A circuit interrupter of the fluid immersed type comprising arelatively stationary contact member having a pair of arcing tipsthereon, a movable contact cooperable with one of said arcing tips toestablish a pressure generating arc, a second movable contact cooperablewith the other of said arcing tips to establish an interrupting arc,means for simultaneously operating said first and said second movablecontacts to substantially simultaneously establish said pressuregenerating and said interrupting arcs, said pressure generating arecausing fluid under pressure to be moved towards said interrupting arcto assist in extinguishing the latter, a hollow piston surrounding saidstationary contact and arranged for reciprocating movement with respectto said stationary contact, spring means for moving said piston in adirection to force fluid under pressure toward said interrupting arc inresponse to an opening movement of said movable contacts, guide meansfor said piston arranged to arrest motion of said piston at a pointbeyond the interrupting arcing tip of said contact member, said pistonduring the circuit opening operation restricting the arcing spaceadjacent the arcing tip of said contact member to assist inextinguishing said interrupting arc, and means associated with saidsecond movable contact for engaging said piston during a closingmovement of said movable contacts to move said piston in the oppositedirection and substantially charge said spring before said movablecontacts make final engagement with their respective arcing tips.

4. In a circuit interrupter of the liquid immersed type, means defininga pressure chamber, means defining an interrupting chamber adjacent tosaid pressure chamber, a relatively stationary contact extending betweensaid chambers, a movable contact operable in said pressure chamber andarranged to coact with said stationary contact to establish a pressuregenerating arc, a second movable contact operable in said interruptingchamber and arranged to coact with said stationary contact to establishan interrupting arc, means for simultaneously operating said movablecontacts to open circuit position to establish said arcs, passagedefining means for di recting liquid under pressure from said pressurechamber toward said interrupting arc, a piston slidably disposed aboutsaid stationary contact and movable relative to said stationary contact,a spring for moving said piston in a direction to force an additionalquantity of liquid toward said interrupting arc, said piston having aninner annular recess for increasing the fluid turbulence adjacent theend of said stationary contact during a circuit opening operation toassist extinguishing said interrupting arc, and means arresting movementof said piston at a point beyond the end of said stationary contactduring the opening movement of said movable contacts, said piston andsaid second movable contact having mutually engageable surfaces adaptedto be brought together during movement of said movable contacts toclosed position to move said piston against said spring to substantiallyfully charge the same prior to the final closing movement of saidmovable contacts.

5. A circuit interrupter of the liquid immersed type comprising meansdefining a pressure chamber, a cylinder having a closed end adjacent tosaid pressure chamber, the other end of said cylinder beingsubstantially open, a stationary contact extending from said pressurechamber into said cylinder through the closed end thereof, a movablepressure generating contact in said pressure generating chamber arrangedto coact with said stationary contact for establishing a pressuregenerating arc, an interrupting contact movable through the open end ofsaid cylinder and cooperable with said stationary contact forestablishing an interrupting arc, means defining liquid flow passagesleading from said pressure chamber to said interrupting arc whereby thepressure created by said pressure generating arc forces liquid intoengagement with said interrupting arc to assist in extinguishing thelatter, an annular piston within said cylinder slidably disposed aboutsaid stationary contact and movable relative to said stationary contact,a spring arranged between the closed end of said cylinder and saidpiston for moving said piston in accordance with an opening movement ofsaid interrupting contact toward the open end of said cylinder to forcean additional quantity of liquid into the region of said interruptingarc, stop means adjacent the open end of said cylinder for arrestingmotion of said annular piston at a point beyond the end of saidstationary contact to provide when thus positioned a restricted arcingspace adjacent said stationary contact, means venting the closed end ofsaid cylinder exteriorly of said pressure chamber, and passage meansthrough said stationary contact providing a by-pass around said pistonto facilitate piston movement, said passage means communicating withsaid venting means to enhance liquid flow through said stationarycontact during a circuit opening operation to assist in extinguishingsaid interrupting arc and for cooling the stationary contact when theinterrupter is in the closed position.

6. In a circuit interrupter, an arc extinguishing unit comprising ahousing forming a pressure generating chamber and having an accessopening therein, covering means releasably secured to said housing fornormally closing said opening, means defining an interrupting chamberdisposed below said pressure chamber, a normally stationary rod-likecontact extending between said chambers, a movable contact operable insaid pressure chamber and arranged to coact with the upper end of saidstationary contact to establish a pressure generating break, a secondmovable contact operable in said interrupting chamber and arranged tocoact with the lower end of said stationary contact to establish aninterrupting break, support means between said chambers having acylindrical bore therein for slidably receiving said stationary contact,and means coacting with said support means whereby said stationarycontact is held against movement in a downward direction beyond apredetermined point, said stationary contact being freely slidable outof said cylindrical bore and being removable through said pressurechamber and through said access opening when said first movable contactis in the open position whereby said stationary contact can be removedwithout disassembling the unit.

WINTHROP M. LEEDS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,760,529 Schwennker May 27, 19302,061,301 Duffing Nov. 17, 1936 2,147,497 Prince et a1 Feb. 14, 19392,235,901 Ronnberg Mar. 25, 1941 2,292,547 Sadler Aug. 11, 19421,918,151 Turnpenny et a1. July 11, 1933 2,273,545 Von Valkenburg Feb.1'7, 1942 1,892,098 Ross Dec. 27, 1932 287,532 Goddard Oct. 30, 18832,095,441 Howe Oct. 12, 1937 2,145,706 Brann Jan. 31, 1939 2,372,589Leeds et a1 Mar. 27, 1945

